1. Field of the Invention
The present invention relates to a lubricating oil composition for a diesel engine and a method for the lubrication of a diesel engine using the same. More specifically, the present invention relates to a lubricating oil composition for a diesel engine having a decreased ash content which can exert excellent engine detergency and deposit-resistant properties without impairing the performance of an exhaust gas post-treatment device such as a particulate exhaust matter (PM) trap or an oxidation catalyst, and a method for the lubrication of a diesel engine which comprises applying the above-mentioned lubricating oil composition as a lubricating oil to the diesel engine provided with the exhaust gas post-treatment device.
2. Description of the Related Art
In recent years, measures to an environmental pollution with nitrogen oxides (NO.sub.x), a particulate exhaust matter (PM) and the like in an exhaust gas from an internal combustion engine, particularly a diesel engine become important themes, and it is an urgent task to decrease the nitrogen oxides and the particulate exhaust matter in the exhaust gas.
As these measures, for the decrease in NO.sub.x, it has be investigated to lower a combustion peak temperature by heightened exhaust gas recycling (EGR) ratio or retarded fuel-injection timing.
However, if the combustion peak temperature is lowered, black smoke and PM increase, and so the installation of an exhaust gas post-treatment device is necessary. As this exhaust gas post-treating device, a PM trap or an oxidation catalyst has been investigated, but both of them have filter structures. Therefore, when a conventional diesel engine oil is used, the problem of clogging (closing) with metals in the oil takes place.
Furthermore, the decrease in the metal content in the oil (the decrease in metal-type detergents) causes the deterioration of detergency, and hence, in order to maintain the present detergency, the development of a novel lubricating oil for the internal combustion engine has been desired.